fix OptInterfaceId (#29)

1 files changed, 3 insertions, 3 deletions

diff --git a/dhcpv6/option_interfaceid.go b/dhcpv6/option_interfaceid.go
index 4ba83f5..2634d9f 100644
--- a/dhcpv6/option_interfaceid.go
+++ b/dhcpv6/option_interfaceid.go
@@ -19,7 +19,7 @@ func (op *OptInterfaceId) Code() OptionCode {
 func (op *OptInterfaceId) ToBytes() []byte {
 	buf := make([]byte, 4)
 	binary.BigEndian.PutUint16(buf[0:2], uint16(OPTION_INTERFACE_ID))
-	binary.BigEndian.PutUint16(buf[2:4], 2)
+	binary.BigEndian.PutUint16(buf[2:4], uint16(len(op.interfaceId)))
 	buf = append(buf, op.interfaceId...)
 	return buf
 }
@@ -33,7 +33,7 @@ func (op *OptInterfaceId) SetInterfaceID(interfaceId []byte) {
 }
 
 func (op *OptInterfaceId) Length() int {
-	return 4 + len(op.interfaceId)
+	return len(op.interfaceId)
 }
 
 func (op *OptInterfaceId) String() string {
@@ -44,6 +44,6 @@ func (op *OptInterfaceId) String() string {
 // The input data does not include option code and length bytes.
 func ParseOptInterfaceId(data []byte) (*OptInterfaceId, error) {
 	opt := OptInterfaceId{}
-	opt.interfaceId = append([]byte(nil), data[4:]...)
+	opt.interfaceId = append([]byte(nil), data...)
 	return &opt, nil
 }